1. Field of the Invention
The present invention relates to a positive crankcase ventilation apparatus which circulates or returns blowby gas from an engine head cover to a surge tank of an intake manifold via a positive crankcase ventilation (PCV) valve.
2. Description of the Related Art
Conventionally, as this kind of apparatus, the following is known. Namely, a PCV valve is mounted or fitted in a penetrating hole which is formed in a head cover. The PCV valve and a circulation port which is formed in a surge tank of an intake manifold are connected together by a blowby gas hose. In this arrangement, the blowby gas hose must be provided, resulting in a higher cost. In addition, the blowby gas hose is exposed to the outside or the external appearance and, therefore, the value of the engine is impaired from an aesthetical viewpoint.
As a solution, the following is known in Japanese Published Unexamined Patent Application No. 229221/1994. Namely, a bottom surface of a surge tank of an intake manifold is arranged to lie close to an upper surface of a head cover. A base end portion of a PCV valve is fitted into a penetrating hole which is formed in the upper surface of the head cover. A top end portion of the PCV valve is fitted into a penetrating hole which is formed in the bottom surface of the surge tank.
In the latter of the above-described prior art, a blowby gas hose becomes needless. It is, however, necessary to attach a grommet for sealing purpose both in the penetrating hole in the head cover and in the penetrating hole in the surge tank. This necessity is a problem in an attempt for further cost reduction. Further, the intermediate portion of the PCV valve is exposed to the external appearance through the clearance between the surge tank and the head cover. Therefore, the quality of the engine from the aesthetic viewpoint has not been completely improved. Still furthermore, if the penetrating hole on the head cover side and the penetrating hole on the surge tank side are not aligned with each other, the PCV valve cannot be successfully fitted in the penetrating holes. To secure a successful fitting of the PCV valve, the machining accuracy of both the penetrating holes is required, resulting in a higher cost.
In view of the above points, the present invention has an object of providing a positive crankcase ventilation apparatus in which the cost and the aesthetic appearance are improved to the maximum extent possible.